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Automated Surface 
Observing System (Asusj 

New Automated Surface Observing 
Systems (ASOS) are currently being 
installed at over 850 locations throughout 
the U.S. The ASOS program is a joint effort 
of the National Weather Service (NWS), 
the Federal Aviation Administration (FAA), 
and the Department of Defense (DOD). 
When installation is completed in the mid- 
1990s, the ASOS systems will serve as the 
nation's primary surface weather 
observing network. ASOS is designed to 
support weather forecast activities and 
aviation operations and, at the same time, 
support the needs of the meteorological, 
hydrological, and climatological research 

With the largest and most modern 
complement of weather sensors, ASOS 
will significantly expand the information 
available to forecasters and the aviation 
community. The ASOS network will more 
than double the number of full-time surface 
weather observing locations. ASOS works 
non-stop, updating observations every 
minute, 24 hours a day, every day of the 

Getting more information on the 
atmosphere, more frequently and from 
more locations, is the key to improving 
forecasts and warnings. Thus, ASOS 
information will help the NWS to increase 
the accuracy and timeliness of its forecasts 
and warnings — the overriding goal of the 
NWS modernization. 

The primary concern of the aviation 
community is safety, and weather 
conditions often threaten that safety. A 
basic strength of ASOS is that critical 
aviation weather parameters are 
measured where they are needed most: 
airport runway touchdown zone(s). 

ASOS detects significant changes, 
disseminating hourly and special 
observations via the NWS and FAA 
communications networks. Additionally, 
ASOS will routinely and automatically 
provide computer-generated voice 
observations directly to aircraft in the vicinity 
of airports, using FAA ground-to-air radio. 
These messages will also be available via 
a telephone dial-in port at the ASOS. 

The ASOS sensors include: ftEfcffttSYL IMm 

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• Cloud Height • Visibility • Precipitation Identification 

• Freezing Rain • Pressure • Temperature/Dew Point JUL xQ ]ggo 
Wind Direction and Speed • Precipitation Accumulation DOCUMENT^ 


ASOS Features 

Observes, formats, archives and transmits ob- 
servations automatically. When preselected 
weather element thresholds are exceeded 
(e.g., the visibility decreases to less than 3 
miles), a "special" report is transmitted. 

Reports basic weather elements: 

• Sky condition: cloud height and amount (clear, 
scattered, broken, overcast) up to 12,000 feet 

• Visibility (to at least 10 statute miles) 

• Basic present weather information: type and 
intensity for rain, snow, and freezing rain 

• Obstructions to vision: fog, haze 

Pressure: sea-level pressure, altimeter setting 

Ambient temperature, dew point temperature 

Wind: direction, speed and character (gusts, 

Precipitation accumulation 

Selected significant remarks including - 
variable cloud height, variable 
visibility, precipitation beginning/ ^ 
ending times, rapid pressure £• 

changes, pressure change ten- 
dency, wind shift, peak wind.